1. Field of the Invention
The present invention relates to a plasma display panel (PDP) and more particularly, to a method of driving a PDP having a preliminary discharge period for applying a preliminary discharge pulse or pulses to scan electrodes, a scan period for applying successively scan pulses to the individual scan electrodes, and a sustain period for applying sustain pulses to the scan electrodes.
2. Description of the Prior Art
PDPs have a lot of advantages such that they can be readily fabricated as large-sized flat display panels, and they can provide a wide field angle of view and quick response. Thus, in recent years, they have been used for flat display devices of various computers, wall-mounted television (TV) sets, public information display panels, and so on.
PDPs are generally classified into two groups with respect to their driving method; the direct current (dc) discharge type and the alternate current (ac) discharge type. In the dc-discharge type, the electrodes are exposed to the discharge space (i.e., the discharge gas) and the PDP is driven by using the dc discharge. The dc discharge is kept for the period when the dc driving voltage is applied. On the other hand, in the ac-discharge type, the electrodes are covered with the dielectric layer not to be exposed to the discharge space (i.e., the discharge gas) and the PDP is driven by using the ac discharge. The discharge is kept by the repetitive polarity reversal of the ac driving voltage.
Since the invention relates to the ac-discharge type PDP, the explanation will be made to only the ac-discharge type PDP.
The ac-discharge type PDP is classified into two groups with respect to the electrode count in each discharge cell or pixel; the two-electrode type and the three-electrode type. A typical example of the three-electrode type PDPs is shown in FIGS. 20 and 21.
FIG. 20 shows the configuration of the discharge cell of the three-electrode type PDP. FIG. 21 shows the layout of the electrodes of this PDP.
As shown in FIGS. 20 and 21, this PDP includes front substrate 20 and a rear substrate 21 fixed together to be opposite to each other. These substrates 20 and 21, each of which are usually made of a glass plate, are arranged parallel to and apart from each other by a specific distance.
A plurality of scan electrodes 22 (i.e., S1, S2, . . . , Sm) are formed to be parallel to each other on the inner surface of the front substrate 20, where m is an integer greater than unity. A plurality of common electrodes 22 (i.e., C1, C2, . . . , Cm) are formed to be parallel to each other on the same inner surface of the front substrate 20. The scan electrodes 22 and the common electrodes 23 extend in the same direction (the lateral direction in FIG. 21) alternately. A transparent dielectric layer 24 is formed on the inner surface of the substrate 20 to cover the scan electrodes 22 and the common electrodes 23. On the dielectric layer 24, a protection layer 25, which is made of MgO, is formed to protect the layer 24 from the discharge.
On the other hand, a plurality of data electrodes 29 (i.e., D1, D2, . . . , Dn) are formed to be parallel to each other on the inner surface of the rear substrate 21, where n is an integer greater than unity. The data electrodes 29 are perpendicular to the scan electrodes 22 and the common electrodes 23. A white dielectric layer 28 is formed on the inner surface of the substrate 21 to cover the data electrodes 29. On the dielectric layer 28, a phosphor layer 27 is formed to emit visual light.
A plurality of partition walls (not shown) are formed to extend parallel to the data electrodes 29 in the space between the front and rear substrates 20 and 21. These walls serve to form the discharge spaces 26 between the substrates 20 and 21 and the display cells or pixels 31. The cells 31 are arranged in a matrix array. A specific discharge gas such as He, Ne, Xe, or the like is confined into the spaces 26.
The above-described PDP configuration has been disclosed in various documents, an example of which is the paper, Society for Information Display (SID) 98 Digest, entitled xe2x80x9cCell Structure and Driving Method of a 25-in. (64-cm) Diagonal High-Resolution Color ac Plasma Displayxe2x80x9d, pp. 279-281, May 1998.
Next, a prior-art driving method of the three-electrode, ac-discharge type PDP shown in FIGS. 20 and 21 is described below. This method is one of the so-called Address Display period Separated sub-field (ADS) methods, which has formed the main stream of methods of this sort.
FIGS. 1A to 1E are waveform charts for explaining this prior-art driving method during one of the sub-fields T1. The sub-field T1 is formed by a preliminary discharge period T2, a scan period T3, and a sustain period T4.
In the preliminary discharge period T2, a preliminary discharge pulse 114 (which is negative here) is commonly applied to the common electrodes 23 (i.e., C1 to Cm). Thus, the difference in wall-charge formation state in the preceding, adjoining sub-field T1 is reset or eliminated for initialization. At the same time as this, ac discharge is caused in all the discharge cells 31 to eliminate the data contained therein, thereby enabling the next writing discharge to occur at a low applied voltage, i.e., enabling the xe2x80x9cpriming effectxe2x80x9d to occur. As a result, the preliminary discharge pulse 114 needs to have an amplitude or voltage level greater than those of the scan pulses and the sustain pulses described later.
One preliminary discharge pulse 114 is used in FIG. 1A. However, two roles of eliminating the difference in wall-charge formation state and of causing the priming effect may be performed by respective pulses. Specifically, a sustain-discharge elimination pulse for resetting the state in the prior sub-field may be applied to the common electrodes 23 (i.e., C1 to Cm) and then, a priming pulse for generating the priming effect in all the cells 31 may be applied thereto. In this case, the count of the sustain-discharge elimination pulses is not limited to unity. It may be two or more.
The priming effect is not necessary for every sub-field. In some driving methods, only a single priming pulse is applied during several successive sub-fields. The priming pulse activates all the cells 31 to emit light independent of whether the cells 31 have displayed information or not. Therefore, if the count of the priming pulses is decreased, the luminance at the time when the cells 31 display black color can be suppressed.
If the preliminary discharge pulse 114 as shown in FIG. 1A is used, to cause a single priming operation during several successive sub-fields, the voltage level or amplitude of the pulse 114 may be set to be low enough for performing only the resetting operation. In this case, to ensure the resetting operation, another pulse or pulses may be applied several times, instead of the pulse 114.
Subsequent to the preliminary discharge pulse 114, a preliminary-discharge elimination pulse 115 (which is negative here) is commonly applied to the scan electrodes 22 (S1 to Sm) in the preliminary discharge period T2. Thus, the wall charge, which have been induced in the dielectric layers 24 and 28 by preliminary discharge due to the preliminary discharge pulse 114, are eliminated or controlled to desired amount.
In FIGS. 1B to 1D, one preliminary-discharge elimination pulse 115 is applied, two or more pulses 115 may be applied to the scan electrodes 22 to ensure the roles of the scan pulses and the sustain pulses, to suppress the fluctuation of the light-emitting state in all the cells 31, and to cope with the load fluctuation for displaying behavior. The preliminary-discharge elimination pulse or pulses 115 may be applied to other electrodes than the scan electrodes 22 also.
Then, in the scan period T3, scan pulses 109 (which are negative here) are successively applied to the respective, scan electrodes 22 (i.e., D1 to Dn), as shown in FIGS. 1B to 1D. Here, a scan bias pulse 112 is kept applied to the scan electrodes 22 in the whole period T3 and the scan pulses 109 are superposed to this bias pulse 112. In response to the scan pulses 109 thus applied, data pulses 110 (which are positive here) are applied to specific ones of the data electrodes 29 according to a required display pattern in this period T3, as shown in FIG. 1E.
In the cells 31 applied with the data pulses 109, a high voltage is applied across the corresponding scan and data electrodes 22 and 29 and therefore, writing discharge occurs. Thus, a large amount of positive wall charge is induced in the dielectric layer 24 covering the scan and common electrodes 22 and 23 while a large amount of negative wall charge is induced in the dielectric layer 28 covering the data electrodes 29. On the other hand, in the cells 31 applied with no data pulses 109, only a low voltage is applied across the corresponding scan and data electrodes 22 and 29 and therefore, writing discharge does not occur and the state of the wall charge that has been formed in the prior sub-field T1 is not changed. As described above, two different states of the wall charge can be generated according to the existence or absence of the data pulse 110.
The slashes (i.e., oblique lines) shown in the data pulses 110 in FIG. 1E denote the fact that the existence or absence of the data pulse 110 changes, according to the display data.
When the application of the scan pulses 109 to all the scan electrodes 22 (S1 to Sm) is completed, the sustain period T4 begins, in which sustain pulses 111 (which are positive) are alternately applied to all the scan electrodes 22 and all the common electrodes 23 (C1 to Cn). The amplitude or voltage level of the sustain pulses 111 are set to be low enough for starting the discharge. Therefore, in the cells 31 where no writing discharge has occurred and the amount of the wall charge has been small or zero, no sustain discharge occurs even if the sustain pulses 111 are applied to the scan or common electrodes 22 or 23.
Unlike this, sustain discharge occurs in the cells 31 where some writing discharge has occurred and a large amount of wall charge has been generated. This is because the first one of the applied sustain pulses 111 (i.e., the first sustain pulse), which is commonly applied to the scan electrodes 22, is added or superposed to the remaining positive wall charge existing in the dielectric layer 24 over the scan electrode side and consequently, a resultant voltage applied across the spaces 26 exceeds the specific discharge-starting voltage. Due to this sustain discharge, negative charge is induced and accumulated on the scan electrode side and at the same time, positive charge is induced and accumulated on the common electrode side.
Next, when the second one of the sustain pulses 111 (i.e., the second sustain pulse) is applied to the common electrodes 23, it is superposed to the remaining positive wall charge existing in the dielectric layer 24 on the common electrode side and consequently, a resultant voltage applied across the spaces 26 exceeds the specific discharge-starting voltage. Thus, opposite-polarity wall charge to that of the first sustain pulse 111 is induced and accumulated on the scan electrode and common electrodes sides, respectively.
Since the above-described steps are repeated in the whole sustain period T4, the sustain discharge is kept during the period T4 in the light-emitting cells 31.
As explained above, the sustain discharge is kept by the phenomenon that the potential difference (or voltage) caused by the wall charge that has been induced by the x-th sustain pulse 111 is superposed to the voltage of the (x+1)-th sustain pulse 111. The count (i.e., the repetition number) of the sustain pulses 111 determines the amount of emitted light.
The combination of the successive sub-fields T1 constitutes the xe2x80x9cfieldxe2x80x9d which is defined as a period for displaying a piece of image information on the display area of the PDP. As described previously, each of the sub-fields T1 is formed by the preliminary discharge period T2, the scan period T3, and the sustain period T4. Thus, if the count of the sustain pulses 111 is changed in each of the sub-fields T1, the display tone (i.e., the intensity levels) on the screen of the PDP can be adjusted optionally.
With the above-explained prior-art method of driving the PDP with reference to FIGS. 1A to 1E, if this method is applied to high-resolution display panels, the scan period T3 needs to be extended or prolonged due to the increase in scan lines (i.e., the count of the scan pulses 109). This means that if the length of the sub-field T1 and that of the preliminary discharge period T2 are fixed, the sustain period T4 needs to be shortened according to the extension of the scan period T3. As a result, there is a problem that the light-emitting period in the sub-field T1 is reduced to thereby lower the luminance of the display screen.
Next, another prior-art driving method of the three-electrode, ac-discharge type PDP shown in FIGS. 20 and 21 is described below. This method also is of the so-called ADS type.
FIGS. 2A to 2E are waveform charts for explaining this prior-art driving method during one of the sub-fields T1. The sub-field T1 is formed by a preliminary discharge period T2, a scan period T3, and a sustain period T4, which is the same as that of the prior-art method of FIGS. 1A to 1E.
In the preliminary discharge period T2, a preliminary discharge pulse 212 is commonly applied to the common electrodes 23 (i.e., C1 to Cm). Thus, the difference in wall-charge formation state in the preceding, adjoining sub-field T1 is reset or eliminated for initialization. At the same time as this, ac discharge is caused in all the discharge cells 31 to eliminate the data written therein, thereby enabling the next writing discharge to occur at a satisfactorily low voltage, i.e., generating the xe2x80x9cpriming effectxe2x80x9d. As a result, the preliminary discharge pulse 212 needs to have an amplitude greater than those of the scan pulses and the sustain pulses described later. This is the same as that described in the prior-art method of FIGS. 1A to 1E.
Similar to the described in the prior-art method of FIGS. 1A to 1E, two roles of eliminating the difference in wall-charge formation state and of causing the priming effect of the pulse 212 may be performed by two pulses. Specifically, a discharge elimination pulse for resetting the state in the prior sub-field T1 may be applied to the common electrodes 23 and then, a priming pulse for generating the priming effect in all the cells 31 may be applied thereto. The count of the discharge elimination pulse may be two or more.
The priming effect is not necessary for every sub-field T1. The priming pulse activates all the cells 31 to emit light independent of whether the cells 31 have displayed information or not. Therefore, if the count of the priming pulses is decreased, the luminance at the time when the cells 31 display a black color can be suppressed.
If the preliminary discharge pulse 212 as shown in FIG. 2A is used, to cause a single priming operation during several successive sub-fields T1, the level or amplitude of the pulse 212 may be set to be low enough for performing only the resetting operation. In this case, to ensure the resetting operation, another pulse may be applied several times, instead of the pulse 212.
Subsequently, a preliminary-discharge elimination pulse 207 is commonly applied to the scan electrodes 22 (S1 to Sm) in the preliminary discharge period T2. Thus, the wall charge, which has been induced in the dielectric layers 24 and 28 by the preliminary discharge, is eliminated or controlled to a desired amount.
In FIG. 2B, a preliminary-discharge elimination pulse 207 is applied, two or more pulses 217 maybe applied to the electrodes 22 to ensure the roles of the scan and sustain pulses, to suppress the fluctuation of the light-emitting state in all the cells 31, and to cope with the load fluctuation for displaying behavior. The preliminary-discharge elimination pulse or pulses 207 may be applied to other electrodes than the scan electrodes 22 also.
Then, in the scan period T3, scan pulses 208 are successively applied to the respective scan electrodes 22 (i.e., S1 to Sm), as shown in FIGS. 2B to 2D. In response to the scan pulses 208, data pulses 209 are applied to specific ones of the data electrodes 29 (i.e., D1 to Dn) according to a required display pattern, as shown in FIG. 2E.
In the cells 31 applied with the data pulses 209, a high voltage is applied across the scan and data electrodes 22 and 29 and therefore, writing discharge occurs. As a result, a large amount of positive wall charge is induced over the scan electrodes 22 and a large amount of negative wall charge is induced over the data electrodes 29. On the other hand, in the cells 31 applied with no data pulses 209, only a low voltage is applied across the scan and data electrodes 22 and 29 and therefore, writing discharge does not occur. Thus, the state of the wall charge is not changed over the scan and data electrodes 22 and 29. Accordingly, two different states of the wall charge can be formed according to the existence or absence of the data pulse 209.
The slashes shown in the data pulses 209 in FIG. 2E denote the fact that the existence or absence of the data pulse 209 changes according to the required display data.
When the application of the scan pulses 208 to all the scan electrodes 22 (S1 to Sm) is completed, the sustain period T4 begins, in which sustain pulses 210 are alternately applied to all the scan electrodes 22 and all the common electrodes 23 (C1 to Cn). Unlike the above-described prior-art method of FIGS. 1A to 1E, the pulses 210 have a negative polarity.
The amplitude or voltage value of the pulses 210 are set to be low enough for preventing the discharge. Therefore, even if the sustain pulses 210 are applied, no discharge occurs in the cells 31 where no writing discharge has occurred in the scan period T3 and as a result, the amount of the wall charge is small. Unlike this, sustain discharge occurs in the cells 31 where some writing discharge has occurred in the scan period T3 and as a result, positive wall charge exists or remains over the scan electrodes 22. This is because the first one of the sustain pulses 210 (i.e., the first sustain pulse) is added or superposed to the remaining positive wall charge and consequently, a voltage higher than the discharge-starting voltage is applied across the space 26, generating the sustain discharge. Due to this sustain discharge, negative charge is induced and accumulated over the scan electrodes 22 and positive charge is induced and accumulated over the common electrodes 23.
Then, the second one of the sustain pulses 210 (i.e., the second sustain pulse) is applied to the common electrodes 23 to induce the above-identified wall charge and then, it is superposed thereto. Thus, opposite-polarity wall charge to that by the first sustain pulse 210 is induced and accumulated over the scan electrodes 22. Subsequently, the same steps are repeated, thereby sustaining the discharge in the light-emitting cells 31.
As described above, similar to the above-described prior-art method of FIGS. 1A to 1E, the sustain discharge is kept by superposing the potential difference caused by the wall charge induced by the x-th sustain discharge to that by the (x+1)-th sustain pulse 210. The count (i.e., the repetition number) of the sustain pulses 210 in the period T4 determines the amount of emitted light.
With the above-explained prior-art method of driving the PDP with reference to FIGS. 2A to 2E, there arises the following problems:
Specifically, since the preliminary discharge pulse 212 is commonly applied to the common electrodes 23 to perform the resetting operation and to cause the priming effect in the preliminary discharge period T2, the voltage applied across the discharge spaces 26 varies dependent upon the state of the wall charge that has been generated in the previous sub-field T1. In other words, the voltage applied across the discharge spaces 26 is equal to a voltage obtained by superposing the wall charge to the applied pulse voltage, in which the amount of the wall charge varies according to whether or not the corresponding cells 31 have emitted light in the previous sub-field T1. Thus, the spaces 26 are applied with different voltages according to the state of the corresponding cells 31 in the previous sub-field T1.
On the other hand, because the level of the priming effect changes according to the voltage applied across the spaces 26, the starting voltage of the subsequent writing discharge in the scan period T3 will vary. As a result, according to whether or not the corresponding cells 31 have emitted light in the previous sub-field T1, there arises a problem that display error tends to occur. For example, some cells 31 that have driven to emit light do not emit light in error, and vice versa.
Moreover, if the sustain elimination pulse and the priming pulse are used in the preliminary discharge period 2, the resetting operation is carried out by the sustain elimination pulse and then, the priming pulse is applied. Therefore, the above problem of error light emission of the cells 31 is difficult to arise. In this case, however, the preliminary discharge period 2 becomes longer and as a result, the scan period T3 needs to be extended. This means that if the length of the sub-field T1 is fixed, the sustain period T4 needs to be shortened by the extension of the preliminary discharge period T2. As a result, there arises another problem that the light-emitting period becomes shorter to lower the luminance of the display screen.
The Japanese Non-Examined Patent Publication No. 6-43829 published in February 1994 discloses a similar driving method of a PDP to the prior-art method of FIGS. 2A to 2E, in which an address period and a sustain period are used for writing the display data into all discharge cells. In the address period, wall charge required for sustain discharge is generated according to the display data. In the sustain period, the sustain discharge is repeated for emitting light. The successive driving for generating the wall charge in the sustain period according to the display data is carried out in the interlaced scanning manner. Thus, the luminance of the display screen is improved and a stable driving state is realized.
FIGS. 3A to 3E are waveform charts for explaining a further prior-art driving method during one of the sub-fields T1. Similar to the prior-art method of FIGS. 2A to 2E, the sub-field T1 is formed by the preliminary discharge period T2, the scan period T3, and the sustain period T4.
In the preliminary discharge period T2, a preliminary discharge pulse 305 is commonly applied to the common electrodes 23. Thus, the difference in wall-charge formation state in the preceding, adjoining sub-field T1 is reset and all the existing wall charge is discharged to be eliminated for initialization. At the same time as this, ac discharge is caused in all the discharge cells 31 to eliminate the data contained therein, thereby enabling the next writing discharge to occur at a low applied voltage, i.e., generating the xe2x80x9cpriming effectxe2x80x9d. As a result, the preliminary discharge pulse 305 needs to have an amplitude greater than those of the scan pulses and the sustain pulses. This is the same as that described in the prior-art method of FIGS. 1A to 1E.
Next, a preliminary-discharge elimination pulse 306 is commonly applied to the scan electrodes 22, eliminating the wall charge existing in the dielectric layer 24 or controlling suitably the amount of this wall charge.
In the scan period T3, scan pulses 307 are successively applied to the scan electrodes 22 while data pulses 308 are suitably applied to the data electrodes 29 according to the display data, causing writing discharge to write the display data into the corresponding cells 31.
In the sustain period T4, sustain pulses 309 are commonly and alternately applied to the scan and common electrodes 22 and 23, emitting light from the corresponding cells 31.
As described above, the sustain discharge is kept by superposing the potential difference caused by the wall charge induced by the x-th sustain discharge to that induced by the (x+1)-th sustain pulse 309. The count (i.e., the repetition number) of the sustain pulses 309 determines the amount of emitted light.
On the other hand, the field, which is a period for displaying a piece of image information on the display area, is formed by a plurality of sub-fields T1. As described previously, each sub-field T1 includes the preliminary discharge period T2, the scan period T3, and the sustain period T4. If the count of the sustain pulses 111 is changed in each sub-field T1, the display tone (i.e., the intensity levels) can be adjusted.
With the above-explained prior-art method of driving the PDP with reference to FIGS. 3A to 3E, the potential of the data electrodes 29 is equal to the ground level (i.e., approximately 0 V) at the time when the positive first sustain pulse 309 is applied to the scan electrodes 22. Therefore, the positive voltage of the first sustain pulse 309 is superposed to the voltage caused by the positive and negative wall charge existing respectively over the scan electrodes 22 and the data electrodes 29 that has been generated by the writing discharge in the scan period T3. As a result, a large voltage is applied across the discharge spaces 26 between the scan and common electrodes 22 and 23. Accordingly, the voltage applied to the discharge spaces 26 between the scan and data electrodes 22 and 29 is higher than that applied to the spaces 26 between the scan and common electrodes 22 and 23. This means that opposing discharge occurs prior to sustain discharge, thereby causing wall charge over the scan electrodes 22. Consequently, the voltage or potential difference between the scan and common electrodes 22 and 23 is lowered to hinder generation of sustain discharge. Thus, there is a possibility that the cells 31 do not emit light in spite of the applied sustain pulses 309.
In this case, the state of the wall charge that has generated in the prior sub-field T1 is difficult to be reset completely, resulting in false emission of light.
Accordingly, an object of the present invention to provide a method of driving an ac-discharge type PDP that ensures a satisfactorily long sustain period even if the count of the scan lines is increased.
Another object of the present invention to provide a method of driving an ac-discharge type PDP that prevents the luminance of the display screen from lowering even if the count of the scan lines is increased.
Still another object of the present invention to provide a method of driving an ac-discharge type PDP that causes the priming effect at approximately the same level independent of whether the pixels or discharge cells have emitted light or not in a prior sub-field.
Still another object of the present invention to provide a method of driving an ac-discharge type PDP that prevents the pixels or discharge cells from emitting light or not in error and that enables the PDP to operate stably.
A further object of the present invention to provide a method of driving an ac-discharge type PDP that ensures the resetting operation of the state of the wall charge or light emission in the previous sub-field in the preliminary discharge period.
A further object of the present invention to provide a method of driving an ac-discharge type PDP that ensures the sustain discharge of the discharge cells that have emitted light in the previous sub-field at the beginning of the sustain period.
The above objects together with others not specifically mentioned will become clear to those skilled in the art from the following description.
According to a first aspect of the present invention, a method of driving an ac-discharge PDP is provided, in which the PDP has row electrodes and column electrodes that form pixels arranged in a matrix array, and a dielectric layer formed to cover the pixels.
The method comprises the steps of:
(a) Scan pulses are applied successively to the row electrodes while data pulses are applied to the column electrodes according to a display signal in a scan period, thereby generating wall discharge in the dielectric layer due to writing discharge.
An amount of the wall charge in each of the pixels varies according to the display signal.
(b) Conversion discharge is caused in a conversion period after the scan period, thereby decreasing the amount of the wall charge in the pixels.
The conversion discharge is caused in a different state in each of the pixels according to the amount of the wall charge.
(c) Sustain pulses are applied to the row electrodes in a sustain period after the conversion period, thereby causing sustain discharge.
The sustain discharge occurs in part of the pixels according to the state of the conversion discharge that has been caused in the conversion period, resulting in emission of light.
With the method according to the first aspect of the present invention, the conversion period is provided between the scan period and the sustain period to cause the conversion discharge, thereby decreasing the amount of the wall charge in the pixels. The conversion discharge is caused in a different state in each of the pixels according to the amount of the wall charge.
Also, the sustain discharge occurs in the sustain period in the part of the pixels according to the state of the conversion discharge that has been caused in the conversion period, resulting in emission of light. In other words, the emission of light from the pixels is determined according to the state of the conversion discharge.
Accordingly, the voltage applied to the row electrodes in the scan period for causing the writing discharge can be raised, which decreases the width of the scan pulses. As a result, even if the count of the scan lines is increased, the length of the scan period can be kept short. This means that a satisfactorily long sustain period is ensured and the luminance of the display screen is prevented from lowering in spite of increase in the count of the scan lines.
In a preferred embodiment of the method according to the first aspect, the writing discharge occurs in the scan period in both of the pixels to emit light and the pixels not to emit light. In this embodiment, there is an additional advantage that the voltage applied to the row electrodes in the scan period for causing the writing discharge can be further raised, which decreases the width of the scan pulses more.
In another preferred embodiment of the method according to the first aspect, a voltage causing the writing discharge in the pixels not to emit light is higher than that in the pixels to emit light. The conversion discharge occurs in the pixels not to emit light and does not occur in the pixels to emit light in the conversion period. In this embodiment, there is an additional advantage that the waveform of the scan pulses can be simplified.
In still another preferred embodiment of the method according to the first aspect, a voltage across the row and column electrodes between which the writing discharge has occurred in the scan period is equal to substantially zero in said conversion period. In this embodiment, there is an additional advantage that the wall charge in the pixels not to emit light can be substantially eliminated and as a result, the margin between the pixels in which the sustain discharge occurs and those in which the sustain discharge does not occur.
In a further preferred embodiment of the method according to the first aspect, a preliminary discharge period for generating a preliminary discharge opposite in polarity to the writing discharge between the row and column electrodes is further provided prior to the scan period. The preliminary discharge is caused by a pulse opposite in polarity to the scan pulses applied to the row electrodes. The preliminary discharge generates preliminary wall charge opposite in polarity to the wall charge generated by the writing discharge in the scan period. In this embodiment, there is an additional advantage that a higher voltage can be applied across the row and column electrodes at the writing discharge and as a result, the length of the scan pulses can be further shortened.
In a still further preferred embodiment of the method according to the first aspect, a first scan bias pulse is commonly applied to the scan electrodes before application of the scan pulses, and a second scan bias voltage is commonly applied to the scan electrodes after application of the scan pulses in the scan period. The first scan bias pulse is equal in polarity to the scan pulses and has an amplitude (or absolute value) less than that of the scan pulses. Alternately, the first scan bias pulse is opposite in polarity to the scan pulses. The second scan bias pulse has an amplitude (or absolute value) greater than that of the first scan bias pulse and less than that of the scan pulses. In this embodiment, there is an additional advantage that error discharge can be prevented from occurring in the scan period.
In a still further preferred embodiment of the method according to the first aspect, the row electrodes are divided into two or more groups. Transition timing from the scan period to the conversion period for the respective groups of the row electrodes is shifted by a specific period. In this embodiment, there is an additional advantage that the peak current that flows in the conversion period can be decreased.
According to a second aspect of the present invention, another method of driving an ac-discharge PDP is provided.
The method comprises the steps of:
(a) A first preliminary discharge pulse is commonly applied to the row electrodes in a preliminary discharge period.
The first preliminary discharge pulse serves to induce discharge only when discharge has occurred in an adjoining, previous sustain period.
(b) A second preliminary discharge pulse is commonly applied to the row electrodes in the preliminary discharge period.
The second preliminary discharge pulse serves to induce discharge only when discharge has not occurred in the adjoining, previous sustain period.
(c) Scan pulses are applied successively to the row electrodes while data pulses are applied to the column electrodes according to a display signal in a scan period subsequent to the preliminary discharge period, thereby generating wall discharge in the dielectric layer due to writing discharge.
(d) Sustain pulses are applied to the row electrodes in a sustain period subsequent to the scan period, thereby causing sustain discharge.
A state of wall charge that has been generated in the adjoining, previous sustain period is reset by the first or second preliminary discharge pulse for initialization in the preliminary discharge period.
With the method according to the second aspect of the present invention, the first preliminary discharge pulse serving to induce discharge only when discharge has occurred in the adjoining, previous sustain period and the second preliminary discharge pulse serving to induce discharge only when discharge has not occurred in the same previous sustain period are applied in the same preliminary discharge period. Thus, the state of the wall charge that has been generated in the adjoining, previous sustain period of the previous sub-field can be reset by the first or second preliminary discharge pulse independent of whether the pixels or discharge cells have emitted light or not in the prior sub-field.
At the same time as this, the existing wall charge can be equalized to each other by the first or second preliminary discharge pulse, even if the amount of the existing wall charge is different at the beginning of the previous discharge period. Therefore, almost the same priming effect can be given independent of whether the cells have emitted light or not in the previous sustain period.
Accordingly, the problem that the cells or pixels emit light or not in error can be solved and the PDP can be operated stably, in which no sustain-discharge elimination pulse is used.
If the PDP is of the three-electrode type having scan electrodes, common electrodes, and data electrodes and at the same time, different amounts of wall charge is generated over these electrodes, respectively, the existing wall charge is difficult to be eliminated by applying a single pulse. In the present invention, the wall charge over the data electrodes is decreased to an approximate zero level. Thus, the elimination of the wall charge generated over the scan, common, and data electrodes can be facilitated, even if the wall charges generated over these electrodes have different amounts.
In a preferred embodiment of the method according to the second aspect, the potential difference or voltage between the row electrodes (e.g., the scan and data electrodes) at a time when the first preliminary discharge pulse is applied is less than that when the second preliminary discharge pulse is applied.
In another preferred embodiment of the method according to the second aspect, the first preliminary discharge pulse is applied to the row electrodes prior to the second preliminary discharge pulse.
In still another preferred embodiment of the method according to the second aspect, the first and second preliminary discharge pulses are applied to the same row electrodes as those applied with the last sustain pulse in the sustain period, thereby reversing the polarity of the potential difference between the row and column electrodes.
In a further embodiment of the method according to the second aspect, the potential difference between the row and column electrodes at a time when the first preliminary discharge pulse is applied is less than that at a time when the second preliminary discharge pulse is applied by a voltage of the sustain pulse. In this embodiment, there is an additional advantage that the first and second preliminary discharge pulses have substantially equal discharge strength, equalizing the levels of the priming effect to each other.
In a further embodiment of the method according to the second aspect, the timing of the preliminary discharge, scan, and sustain periods for all the cells are equal to each other.
In a further embodiment of the method according to the second aspect, the row electrodes of the PDP includes common electrodes and scan electrodes and the column electrodes thereof include data electrodes. The common electrodes and the scan electrodes extending parallel to each other. The data electrode extend perpendicular to the scan and common electrodes. This means that the PDP is of the three-electrode type. In this case, it is preferred that the first and second preliminary discharge pulses are commonly applied to the scan and common electrodes. There arises an additional advantage that the amount of the wall charge generated by the sustain pulse in the prior sub-field can be adjusted to a suitable value by the first preliminary discharge pulse.
In a further embodiment of the method according to the second aspect, the potential or voltage of the data electrodes is set at a value existing between the potentials or voltages of the scan electrodes and the common electrodes. There is an additional advantage that the amount of the wall charge generated over the data electrode can be decreased.
In a further embodiment of the method according to the second aspect, the potential difference or voltage between the scan and data electrodes is set to be equal to approximately half of the potential difference or voltage between the scan and common electrodes. There is an additional advantage that the subsequent wall-charge elimination can be facilitated, which decreases the necessary number of the wall-charge-elimination pulses.
In a further embodiment of the method according to the second aspect, the potential or voltage of the data electrodes in the preliminary discharge period is equal to one of two potential or voltage values of the data electrodes according to whether the cells emit light or not in the scan period. There is an additional advantage that the setting of voltage of the data driver is unnecessary.
In a further embodiment of the method according to the second aspect, the potential or voltage of the data electrodes the preliminary discharge period is set to be approximately equal to the ground level. There is an additional advantage that the voltage values of the first and second preliminary discharge pulses can be lowered.
In a further embodiment of the method according to the second aspect, in the preliminary discharge period, a preliminary-discharge elimination pulse is applied to the row electrodes after the first and second preliminary discharge pulses are applied. The preliminary-discharge elimination pulse has a waveform that varies gradually its voltage value to reach a peak voltage value. The peak voltage value is substantially equal to a potential difference or voltage between the row and column electrodes at a time when the first or second preliminary discharge pulse is applied.
According to a third aspect of the present invention, another method of driving an ac-discharge PDP is provided, in which the PDP has scan electrodes and common electrodes and data electrodes. The common electrodes and the scan electrodes extending parallel to each other, and the data electrode extend perpendicular to the scan and common electrodes, thereby forming pixels arranged in a matrix array.
The method comprises the steps of:
(a) Scan pulses are applied successively to the scan electrodes while data pulses are applied to the data electrodes according to a display signal in a scan period, thereby causing writing discharge.
(b) Sustain pulses are alternately applied to the scan electrodes and the common electrodes in a sustain period subsequent to the scan period, thereby causing sustain discharge for light emission.
When a first one of the sustain pulses is applied to the scan electrodes or the common electrodes in the sustain period, a voltage applied across the scan electrodes and the data electrodes is set to be lower than a voltage applied across the scan electrodes and the common electrodes.
With the method according to the third aspect of the present invention, because of the following reason, sustain discharge of the discharge cells that have emitted light in the previous sub-field at the beginning of the sustain period is always induced, and as a result, the resetting operation of the state of the wall charge or light emission in the previous sub-field is ensured.
In general, discharge starts after the application of a voltage by a specific time lag or delay time, where the time lag varies dependent on the applied voltage. The time lag becomes shorter as the applied voltage increases.
With the method according to the third aspect, when the first one of the sustain pulses is applied to the scan electrodes or the common electrodes in the sustain period, the voltage applied across the scan electrodes and the data electrodes is set to be lower than the voltage applied across the scan electrodes and the common electrodes. Therefore, at the beginning of the sustain discharge, surface discharge can be caused between the scan and common electrodes before opposing discharge occurs between the scan and data electrodes. Thus, sustain discharge surely occurs in the pixels where writing discharge has occurred in the previous sub-field by the first one of the sustain pulses, which means that false emission of light is prevented and at the same time, the resetting operation of the state of the wall charge or light emission in the previous sub-field is carried out.
Moreover, since large driving margin can be set for the scan and sustain voltages or the like, the false emission of light that is induced by the state of emitting light or not in the neighboring pixels, can be prevented even if the scan pulse voltage and/or the sustain pulse voltage fluctuate.
In a preferred embodiment of the method according to the third aspect, the voltage level of the data electrodes is approximately equal to that of the data pulses when the first one of the sustain pulses is applied. The voltage level of the data electrodes is kept at an approximately ground level after the first one of the sustain pulses is applied. Second to last ones of the sustain pulses have positive and negative polarities, and are alternately applied to the scan electrodes and the common electrodes.
In this embodiment, there is an additional advantage that the potential difference or voltage between the scan electrodes and the common electrodes can be set lower than that in the prior-art method of FIGS. 3A to 3E, when the first one of the sustain pulses are applied. Thus, the wall charge over the data electrodes that have been generated by the writing discharge in the scan period can be eliminated, facilitating the sustain discharge by the first one of the sustain pulses.
Also, if the amount of the wall charge over the data electrodes is adjusted to a suitable value in the sustain period, only the wall charges existing over the scan and common electrodes can be adjusted due to discharge in a preliminary discharge period.
Moreover, for example, if the potential of the data electrodes is set as zero (V) at the time when no data pulse is applied, two values of 0 and the data pulse voltage are necessary in the data driver. However, in this case, there is an additional advantage that the PDP can be driven by a two-value driver without any other voltage value or values.
In another preferred embodiment of the method according to the third aspect, the voltage level of the data electrodes is approximately equal to that of the data pulses when the first one of the sustain pulses is applied. The voltage level of the data electrodes is kept at an approximately ground level after the first one of the sustain pulses is applied. The second to last ones of the sustain pulses have a positive polarity only, and are alternately applied to the scan electrodes and the common electrodes.
In this embodiment, there is the same additional advantage as above that the potential difference or voltage between the scan electrodes and the common electrodes can be set lower than that in the prior-art method of FIGS. 3A to 3E, when the first one of the sustain pulses are applied.
In still another preferred embodiment of the method according to the third aspect, the voltage level of the data electrodes is approximately equal to that of a ground level in the whole sustain period. The first one of the sustain pulses has a negative polarity for the scan electrodes and a ground level for the common electrodes. The second to last ones of the sustain pulses have positive and negative polarities, and are alternately applied to the scan electrodes and the common electrodes.
In this embodiment, there is the same additional advantage as above.
In a further preferred embodiment of the method according to the third aspect, the voltage level of the data electrodes is kept approximately equal to that of the data pulses in the whole sustain period. The first one of the sustain pulses has a positive polarity for the scan electrodes and a negative polarity for the common electrodes. The second to last ones of the sustain pulses have a positive polarity, and are alternately applied to the scan electrodes and the common electrodes.
In this embodiment, there is the same additional advantage as above.
In a still further preferred embodiment of the method according to the third aspect, the voltage level of the data electrodes is kept approximately equal to that of a ground level in the whole sustain period. The first one of the sustain pulses has a ground level for the scan electrodes and a negative polarity for the common electrodes. The second to last ones of the sustain pulses have a positive polarity, and are alternately applied to the scan electrodes and the common electrodes.
In this embodiment, there is the same additional advantage as above.
In a still further preferred embodiment of the method according to the third aspect, the voltage level of the data electrodes is approximately equal to that of a ground level when the first one of the sustain pulses is applied, and is kept approximately equal to that of the data electrodes after the first one of the sustain pulses is applied. The first one of the sustain pulses has a ground level for the scan electrodes and a negative polarity for the common electrodes. The second to last ones of the sustain pulses have a positive polarity, and are alternately applied to the scan electrodes and the common electrodes.
In this embodiment, there is the same additional advantage as above.
In a still further preferred embodiment of the method according to the third aspect, the voltage level of the data electrodes is approximately equal to that of a ground level in the whole sustain period. The first one of the sustain pulses has a ground level for the scan electrodes and a negative polarity for the common electrodes. The second to last ones of the sustain pulses have a positive polarity, and are alternately applied to the scan electrodes and the common electrodes.
In this embodiment, there is the same additional advantage as above.